Process for preparing cephalosporins with salified intermediate

ABSTRACT

Cephalosporins may be conveniently prepared by a process in which 7-ACA is silylated, acylated, desilylated and then salified to give an intermediate which is eventually cyclized with thiourea.

FIELD OF THE INVENTION

Numerous cephalosporins of formula (I)

characterised by the 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic chainin position 2 of the 7-ACA, and its derivatives of formula (II)

are known in which R² can have various meanings including CH₂OCOCH₃ inthe case of 7-ACA, the cefotaxime nucleus or

in the case of 7-ACT, the ceftriaxone nucleus, or

in the case of Furaca, the ceftiofur nucleus.

BACKGROUND OF THE INVENTION

Each of these cephalosporins, including those having a different meaningof R¹ and R², has been invented and synthesized with its own synthesismethod, so that initially there was no common method suitable forproducing all cephalosporins having the2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic chain.

DESCRIPTION OF THE RELATED ART

Recently, in 1996, U.S. Pat. No. 5,583,216 was granted (the filing dateof which however was many years previously), generically covering anyprocess usable for inserting the aforesaid chain into 7-ACA and itsderivatives. In this manner, any cephalosporin included in the aforesaidgroup falls within the scope of protection of U.S. Pat. No. 5,583,216for what concerns the methods used up to the present time for itsproduction, even if that cephalosporin was invented many years prior tothe granting of U.S. Pat. No. 5,583,216: however in truth, this patentdoes not describe any process which can be applied industrially forproducing cephalosporins.

To avoid U.S. Pat. No. 5,583,216, considerable research has been carriedout, leading inter alia to the granting of U.S. Pat. No. 6,458,949 whichclaims the intermediate of formula (A)

in which X is Cl or Br, usable for preparing ceftiofur by cyclizationwith thiourea.

This intermediate is always precipitated in acid form from a solution inmethylene chloride at 2-5° C., filtered off, washed with cold water (5°C.) and then with methylene chloride. In fact, considering that theprecipitate originates from a solution in methylene chloride, accordingto the usual technique it would have been logical to expect the firstwash to have been effected with the same solvent, the water wash beingeffected only later. This reversal of the wash order and the use of coldwater is therefore not random, but points to the fact that theintermediate does not possess great stability and that the water-solubleacid impurities which impregnate the solid just filtered off must berapidly removed. In addition the intermediate claimed in U.S. Pat. No.6,458,949, again in acid form, is dried before subsequent cyclizationwith thiourea, as this reaction is carried out in water-tetrahydrofuranand it is advisable to remove methylene chloride residues. Moreover themaximum obtainable yield is only 75%. U.S. Pat. No. 6,552,186 claims acompound of formula (IV)

in which X is halogen, R³ is trialkylsilyl and R² is

This compound is reacted with silylated thiourea to provide a compoundof formula (I) in which R¹ and R² have the aforesaid meanings and whichon subsequent hydrolysis gives the compound having the same formula (I)but in which R¹ is H and R² is as aforestated: this compound isceftriaxone.

U.S. Pat. No. 6,522,186 hence provides a compound of formula (IV) inwhich R³ is trialkylsilyl. The corresponding derivative in which R³ ishowever H had already been described in U.S. Pat. No. 4,458,072 andobtained as an amorphous product (column 16, line 49) without anyindication of the yield, by a laborious process using a precipitatingagent such as petroleum ether: this method is certainly unsuitable forindustrial use. Again, U.S. Pat. No. 6,552,186 says nothing aboutyields, as the claimed process comprises direct obtaining of thesilylated product of formula (IV) and subsequent reaction with silylatedthiourea to give silylated ceftriaxone: the final passage to obtainceftriaxone disodium salt takes place by the known methods, howeveroverall total process yields are not given.

The recent U.S. Pat. No. 6,458,949 claims a process by which Furaca issilylated and then reacted with a compound of formula (III)

in which X is Cl or Br and Y is Cl, orO—CH═N+(CH₃)₂Cl⁻

-   -   to isolate an aforestated compound of formula (A), in which X is        Cl or Br and the carboxyl is free, non-salified and        non-esterified.

When reacted with thiourea in a partly aqueous solvent, thisintermediate produces ceftiofur.

Compounds of formula (III) have been known for some time: for example,GB 2,012,276 describes in example 5 the preparation of a compound offormula (III) in which the methoxyimino group is substituted by theethoxyimino group, X is Br and Y is Cl, by reacting the correspondingacid having the same formula (III) but in which X is Br and Y is OH,with PCl₅ in a dichloromethane solution. According to example 13 of thepatent, 7-(4-chloro-3-oxo-2-methoxyiminobutyryl-amino)cephalosporanicacid is subsequently reacted with thiourea to give a sodium salt of7-[2-(2-aminothiazol-4-yl)-2-methoxyiminoacetamido)cephalosporanic acid,this being cefotaxime, EP 30294 (page 4, lines 36-37 and 40-45), U.S.Pat. No. 6,384,215 (column 3, lines 19-20) and U.S. Pat. No. 6,458,949(column 4, line 1; column 5, line 2 and lines 47-48) also describe thepreparation of compounds of formula similar to formula (III).

It is therefore apparent that compounds of formula (III) in activatedform, able to react with a compound of formula (II) silylated at thecarboxyl, can be prepared for example as chlorides by reaction with PCl₅or other chlorinating agents, such as POCl₃ and DMF, in dichloromethane.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process of highefficiency in terms of final product yield and purity, for producingceftiofur, cefotaxime, ceftriaxone, and cephalosporins generally,characterised by the same general formula (I)

in which R¹ is H or Na and R² is chosen from the group consisting of H,CH₃, CH₂OCH₃, CH₂OCOCH₃, CH═CH₂,

According to this process, a compound of formula (II)

in which R² has the aforestated meanings is silylated at the carboxyl togive the corresponding trialkylsilyl-ester which is reacted with acompound of formula (III)

in which X is Cl or Br and Y is Cl, orO—CH═N⁺(CH₃)₂ Cl⁻to give a cephalosporin of formula (V)

in which X and R² have the aforestated meanings, and R³ istrialkylsilyl, which is hydrolyzed at pH 7÷7.5 and then treated in apartly aqueous solution with benzathine or a salt thereof, to obtaincrystallization of a new cephalosporin of formula (V)

where Z is benzathine, in which the carboxyl is salified by thebenzathine, this salt being filtered off, washed with water and reactedin a partly aqueous solvent with thiourea, to lead to the formation ofthe 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic chain and give asolution of the compound of general formula (I) in which R² has theaforestated meanings and R¹ is H, the compound of formula (I) beingcrystallized from this solution in the form of the sodium salt, of thesalt of a pharmaceutically acceptable inorganic acid or of an internalsalt.

Simultaneously with the formation of the2-(2-aminothiazol-4-yl)-2-methoxyyminoacetic chain there may be theprecipitation of benzathine hydrochloride which is filtered off andremoved to leave a very pure solution of the compound of general formula(I).

In particular, it has been surprisingly found possible to quantitativelyisolate in aqueous solution a cephalosporin of formula (V), in which R²is CH₂OCOCH₃, or

without any interaction with the halogen atom X present in the compoundsof formula (V).

This precipitation, in aqueous solution automatically eliminates all theacid impurities originating from the preparation of the aforesaidcompounds of formula (V), then by simply washing with water a highpurity moist product is obtained ready for subsequent reaction withthiourea in a partly aqueous environment.

A further considerable advantage of the present invention derives fromthe fact that the cyclization reaction with thiourea, leading to theformation of HCl, finds in benzathine a base able to subtract it fromthe solution as the hydrochloride insoluble under reaction conditions.In this manner a solution is obtained containing only cephalosporin inacid form of such purity as to enable it to be very easily crystallizedas the sodium salt, by adding a sodium salt such as sodium acetate orsodium 2-ethyl-hexanoate.

This succession of operations will be more apparent from thenon-limiting examples which follow.

However, the same operative scheme can evidently be applied for theproduction of cephalosporins other than ceftiofur, cefotaxime andceftriaxone, having nuclei different from the aforespecified three, buthaving the same 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic side chainin position 7.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLE 1 Preparation of SodiumCeftiofur

Two separate solutions are prepared.

Solution A

40 g of FURACA (MW 340.38-0.118 moles) and 336 ml of tetrahydrofuran arefed into a dry 1 litre flask under a nitrogen flow in the absence ofdirect light. The mixture is agitated for 15 minutes untilhomogenization, while cooling in the meantime to +10° C.

While maintaining the temperature at +10° C.÷+12° C., 1.486 ml oftrimethylchlorosilane (MW 108.64-d=0.859-0.1 eq) are quickly added. Themixture is agitated for 5 min at +10° C.÷+12° C., and 45.43 g ofN,O-bis-trimethylsilyl-acetamide (MW 203.43-d=0.832-1.9 eq) are addedover 5÷10 minutes.

The temperature is raised to +20° C. and the mixture agitated for 1 h35min at 22° C.÷23° C. until a solution is obtained. It is cooled to −35°C.÷−40° C.

Solution B

210 ml of ethyl acetate and 13.02 ml of N,N-dimethylformamide (MW73.094-0.169 moles-d=0.95-12.37 g) are fed into a dry 1 litre flaskunder a nitrogen flow.

15.49 ml of phosphorus oxychloride (POCl₃) (0.167 moles-MW153.33-d=1.675-25.95 g) are added at +25° C., allowing the temperatureto rise to +36° C.

The mixture is cooled to 0° C. and 27.62 g of4-chloro-3-oxo-2-methoxyimino-butyric acid, commonly known as COMBA (MW179.56-0.154 moles) are added without exceeding +5° C. The mixture isagitated for 1 hour at +5° C.

Solution B is added dropwise to solution A over 15 minutes maintainingthe temperature at −35° C.÷−40° C. The reaction terminates within 2hours at −35° C.÷−40° C.

On termination of the reaction the mixture is poured into 500 ml ofwater at 0° C., maintaining the pH at 7.0÷7.5 with triethylamine, whilemaintaining the temperature at 0° C. 200 ml of ethyl acetate are addedand the phases are separated at 0° C. ÷+5° C. Extraction is againeffected at pH 7.0÷7.5 with 350 ml of water.

The aqueous phase is decolorized at 0° C.÷+5° C. for 30 minutes with 4 gof carbon and 0.4 g of EDTA. It is filtered and washed with 150 ml ofwater.

The pH is adjusted to 7.0÷7.5 with triethylamine at 0° C.÷+5° C. using atotal of 110 ml thereof.

A mixture of 43.25 g of benzathine diacetate (0.120 moles) dissolved in350 ml of water is added dropwise, then washing with 50 ml of water.

It is left to precipitate cold at 0° C.÷+5° C. for about 90 minutes.

The precipitate is filtered off and washed with 500 ml of water dividedinto two portions. It is left to drip well.

The condensation product of 7-FURACA with activated COMBA, precipitatedmoist as benzathine salt, is used as such in the next passage.

A sample is dried for analysis.

The moist benzathine salt obtained as described is suspended in 740 mlof tetrahydrofuran at +20° C.÷+25° C.

It is cooled to 0° C.÷+5° C. and 19 ml of triethylamine are added,maintaining this temperature. 12 g of thiourea are added at 0° C.÷+25°C. and the mixture agitated for 18 hours.

It is cooled to 0° C.÷+5° C. and, while maintaining this temperature,600 ml of ethyl acetate are added plus about 20 ml of concentratedhydrochloric acid to pH 3. The precipitated benzathine hydrochloride isfiltered off and the filter washed with a mixture of 60 ml oftetrahydrofuran +60 ml of ethyl acetate.

400 ml of water are added to the filtrate solution.

The temperature is raised to +10° C.÷+15° C. and the pH adjusted to8.0÷8.5 with 15 ml of triethylamine.

The phases are separated.

The impoverished organic phase is re-extracted with a further 400 ml ofwater at pH 8.08.5, the aqueous phases are pooled and washed with 300 mlof ethyl acetate. 400 ml of tetrahydrofuran are added to the aqueousphase.

The mixture is cooled to 0° C.÷+5° C. and the pH adjusted to 3 with 1Nhydrochloric acid. 300 g of sodium chloride are added and the mixtureagitated until a solution forms, while raising the temperature to +15°C.÷+20° C.

The phases are separated, the overlying organic phase being rich inproduct. Carbon is added to the organic phase at +15° C.÷+20° C. and themixture agitated for 20 minutes. The mixture is filtered and washed with100 ml of tetrahydrofuran.

A homogeneous mixture of 28.88 g of sodium 2-ethylhexanoate and 100 mlof tetrahydrofuran is added dropwise to the decolorized organic phaseover 20 minutes.

The mixture is agitated for 15 minutes at +15° C.÷+20° C.

The solution obtained is added dropwise over 30 minutes to 1000 ml ofagitated tetrahydrofuran at +20° C.

The mixture is agitated for 2 hours at +20° C., filtered and washed with320 ml of acetone.

The product is dried at +30° C.÷+32° C. to obtain 51.3 g of sodiumceftiofur.

The dried sample of benzathine salt has the following general formula(V), and more specifically has the general formula

which provides the following spectra:

¹HNMR in DMSO-d₆ 300 Mhz; Hc=9.40 ppm 1H; Hn=8.04 ppm 1H;Hu-Hv=7.32-7.46 ppm 10H; Hl=7.39 ppm 1H; Hm=6.77 ppm 1H; Hd=5.68 ppm 1H;He=5.06 ppm 1H; Hq-Hr=4.84 ppm 3H; Hb=3.95 ppm 3H; Hh-Hi=4.22-3.99 ppm2H; Hf-Hg=3.65-3.26 ppm 2H; Hs-Ht=4.03 ppm 4H; Ho-Hp=2.95 ppm 4H;Ha=3.97 ppm 2H.

FT-IR (cm¹); 1777.6-1717.1-1650.7-1565.8

EXAMPLE 2 Preparation of Ceftriaxone Disodium Salt

Two separate solutions are prepared.

Solution A

15.57 g of 7-ACT (MW 371.39-0.042 mol) and 155 ml of methylene chlorideare fed into a dry 1 litre flask under a nitrogen flow in the absence ofdirect light. The mixture is cooled to +10° C. and 34.11 g ofN,O-bis-trimethylsilyl-acetamide are added, a slight amount of heatbeing produced. The mixture is agitated at +20÷22° C. and after 45minutes a complete solution is obtained. The mixture is cooled to −40°C.

Solution B

80 ml of ethyl acetate and 4.69 ml of N,N-dimethylformamide (MW 73.09,d=0.95) are fed into a dry 1 litre flask under a nitrogen flow at +25°C. 5.58 ml of phosphorus oxychloride (MW 153.33, d=1.675, 9.34 g) areadded allowing the temperature to rise to 36° C. (if this temperature isnot attained within 20÷25 minutes, heating is required). The mixture iscooled to 0° C. then 9.94 g of 4-chloro-3-oxo-2-methoxyimino-butyricacid, commonly known as COMBA (MW 179.56) are added. The mixture isagitated at +5° C. for 1 hour. Solution B is added dropwise to solutionA over 15÷20 minutes maintaining the temperature at −35°÷−40° C. andwashing the flask with 15 ml ethyl acetate. The mixture is agitated for10 minutes at −35°÷−40° C. and the reaction goes to completion. Thereaction mixture is poured into a mixture of 50 ml water, 320 mlisopropanol and 270 ml of a saturated aqueous solution of sodiumbicarbonate pre-cooled to 0°÷+5° C. without exceeding +5° C. It isagitated for 2 hours at 0°÷+5° C. maintaining the pH at 2.5 (consumingabout 27 ml of 17% hydrochloric acid), the pH being checked for about 90minutes, during which any necessary correction is done with solid sodiumbicarbonate. The phases are separated and the underlying aqueous phaseis retained. The rich organic phase is washed with 25 ml water, thenwith a solution of 22 g NaCl in 80 ml water. The aqueous phases areretained each time and pooled, then re-extracted with 40 ml methylenechloride. The organic phases are pooled and the spent aqueous phase isdiscarded. The former is decolorized under agitation for 15 minutes with1.5 g carbon, filtered and the filter is washed with 30 ml of methylenechloride. 150 ml of water are added to the decolorized organic phase at0°÷+5° C. followed by, still at 0°÷+5° C., a solution of 11.21 ganhydrous sodium acetate in 100 ml water pre-cooled to 0°÷+5° C. After30 minutes the phases are separated allowing the temperature to rise toabout +20° C. The poor organic phase is re-extracted with 100 ml ofwater, facilitating separation with 50 ml of methylene chloride. Theaqueous phases are pooled and decolorized at +20° C. for 30 minutes with1.5 g of carbon, 0.150 g of EDTA and 0.200 g of celite. The mixture isfiltered and the filter is washed with 100 ml water.

A solution of 15.14 g of benzathine diacetate in 160 ml demineralisedwater is added over 15 minutes to the decolorized solution at 15°÷20° C.The mixture is agitated for 30 minutes at 15°÷20° C., cooled to 0°÷+5°C. and agitated for 1 hour. It is filtered and washed 3 times with 50 mlof water. It is thoroughly squeezed under a nitrogen flow to obtain28.52 g of the benzathine salt of the condensation product of 7-ACT withCOMBA. A sample is dried for analysis.

The dried sample of benzathine salt has the general formula (V), andmore specifically has the formula

which provides the following spectra:

¹HNMR in DMSO-d₆ 300 MHz: Hc=9.36 ppm 1H; Hu-Hv=7.30-7.42 ppm 10H;Hd=5.65 ppm 1H; He=5.03 ppm 1H; Ha-Ha′=4.84 ppm 3H; Hb=4.03 ppm 3H;Hq-Hr=3.91 ppm 3H; Hh-Hi=4.35-4.12 ppm 2H; Hm=3.50 ppm 3H;Hf-Hg=3.62-3.39 ppm 2H; Hs-Ht=3.53 ppm 4H; Ho-Hp=2.89 ppm4H.

FT-IR (cm⁻¹): 1775.1-1715.7-1666.6-1594.1

The benzathine salt obtained is suspended in 200 ml water and 142 g ofthe sulfonic resin Resindion UBK 530 in sodium form and 6.38 g ofthiourea are added at 20°÷25° C. The mixture is agitated for 4 hours at20°÷25° C., filtered and washed 8 times with 50 ml of water each timeand then decolorized for 20 minutes at 15°÷20° C. with 1.5 g of carbon,0.150 g of EDTA and 0.200 g of celite. The carbon is filtered off andthe filter is washed 4 times with 50 ml water. The pH is adjusted toabout 4.2 with 7 ml of 17% hydrochloric acid at 15°/20° C., untilprecipitation begins. It is agitated for 30 minutes, and adjusted to pH3 over 40 minutes at 15°÷20° C. with about 13 ml of 0.17% hydrochloricacid.

It is filtered off, washed twice with 50 ml water and thoroughlysqueezed to obtain 45 g of crude ceftriaxone acid (K.F.=about 60%).

79.5 ml of acetone, 20 ml of water, 80 g of carboxylic resin RELITE CNS(activated in sodium form) are fed into a flask. The mixture is cooledto +10° C. and 45 g of well-sifted crude ceftriaxone acid obtained aboveare added, then agitated at +10° C. for 4 hours until the dissolvedceftriaxone content remains constant. The resin is filtered off, washedwith a mixture of 10 ml water+8 ml acetone and then with a mixture of 6ml water and 19 ml acetone, maintaining these washes separate from theinitial filtrate and at +10° C. The initial filtrate is maintained underagitation with 1.33 g carbon, 0.07 g EDTA and 0.13 g celite, for 45minutes at +10° C. This is filtered off and washed with the mixture ofthe two washes kept separate from the initial filtrate, the decolorizedsolution being diluted with 79.5 ml acetone added dropwise over 10minutes at +10° C. It is seeded with disodium ceftriaxone and agitatedfor 90 minutes at +10° C. 291.5 ml of acetone are then added dropwiseover 3 hours at +10° C. The product is filtered off and washed with 106ml portions of acetone, thoroughly squeezed under a nitrogen flow thendried at ambient temperature until constant weight, to obtain 22.5 gdisodium ceftriaxone.

EXAMPLE 3 Preparation of Cefotaxime Sodium Salt

Two separate solutions are firstly prepared.

Solution A

64 g of 7-ACA (MW 272.28-0.235 mol) and 400 ml of tetrahydrofuran arefed into a dry 1 litre flask under a nitrogen flow and in the absence ofdirect light. The mixture is agitated for 15 minutes until homogenizedwhile cooling to +15° C.

191.34 g of N,O-bis-trimethylsilyl-acetamide (MW 203.43, d=0.832, 0.941mol) are quickly added, maintaining the temperature at 20°÷25° C. Thetemperature is maintained at 20°÷25° C. while the mixture is agitatedfor 15 minutes at +20°÷+25° C. until dissolved, then cooled to −35°C.÷−40° C.

Solution B

420 ml of ethyl acetate and 26.04 ml of N,N-dimethylformamide (MW 73.09,d=0.95, 0.338 mol, 24.74 g) are fed into a dry 1 litre flask under anitrogen flow at +25° C. 30.98 ml of phosphorus oxychloride (MW 153.33,d=1.675, 51.9 g) are added allowing the temperature to rise to 36° C.(if this temperature is not attained in 20÷25 minutes, heating isrequired). The mixture is cooled to 0° C. then, without exceeding +5°C., 55.24 g of 4-chloro-3-oxo-2-methoxyimino-butyric acid, commonlyknown as COMBA (MW 179.56-0.308 mol) are added. The mixture is agitatedat +5° C. for 1 hour. Solution B is added dropwise into solution A over15÷20 minutes while maintaining the temperature at −35°÷−40° C.

The reaction terminates within about 45 minutes at −35°÷−40° C. At theend of the reaction 600 ml of water at 0° C. are poured in, adjustingthe pH to 7÷7.5 with triethylamine and maintaining the temperature at0°÷+5° C.

The organic phase is extracted again with 450 ml of water at 0°÷+5° C.,maintaining the pH at 7÷7.5.

The aqueous phases are pooled and a solution of 85.05 g of benzathinediacetate in 800 ml of water is added dropwise over 60 minutes,maintaining the temperature at 0°÷+5° C. It is agitated for 1 hour at0°÷+5° C., the product is filtered off then washed twice with 250 mlwater and thoroughly squeezed. 152 g of moist condensation product of7-ACA with COMBA as the benzathine salt are obtained.

A sample is dried for analysis.

The dried sample of benzathine salt has the general formula (V) and morespecifically has the formula

which provides the following spectra:

¹HNMR in DMSO-d₆ 300 MHz: Hc=9.42 ppm 1H; Hu-Hv=7.36-7.46 ppm 10H;Hd=5.73 ppm 1H; He=5.03 ppm 1H; Hq-Hr=4.85 ppm 3H; Hb=3.95 ppm 3H;Hh-Hi=4.11-4.03 ppm 2H;

Hf-Hg=3.55-3.36 ppm 2H; Hs-Ht=3.99 ppm 4H; Ho-Hp=3.05 ppm 4H; Ha=2.03ppm 2H.

FT-IR (cm⁻¹): 1766.3-1719.5-1660.0-1555.8

The moist product obtained is suspended in a mixture of 320 ml oftetrahydrofuran and 80 ml of water, cooled to 0°÷−5° C. and 22 ml oftriethylamine are added to pH 7.5. 24.84 g of thiourea are added andleft to react for 4 hours at +20°÷+25° C. until conversion of theaforestated condensation product to cefotaxime is complete.

On termination of the reaction 1.6 g of sodium hydrosulfite, 0.4 g ofEDTA, 0.8 g of celite and 4 g of carbon are added and the mixture isagitated for 20 minutes then filtered, washing the product with 80 ml oftetrahydrofuran. The tetrahydrofuran is evaporated under reducedpressure until an oily residue forms. 368 ml of water are added dropwiseto the oil obtained under agitation.

233.6 g of 99% formic acid are dropped over a period of 5÷10 minutes at+15°÷+20° C. into the suspension obtained.

It is cooled to 0°÷+5° C. and agitated for 3 hours, filtered and theproduct washed with 96 ml of water pre-cooled to 0°÷+5° C. The productis suspended in 384 ml of ethanol at 45÷50° C. and agitated for 1 hour.It is filtered off while hot then washed with 192 ml of ethyl acetate.

After drying, 36 g of cefotaxime ethanol solvate with a concentration of85% is obtained, serving as intermediate.

227.5 ml of methanol, 28.2 ml of water and 32.8 g of sodium2-ethylhexanoate are fed into a flask under a nitrogen flow. The mixtureis agitated at ambient temperature until completely dissolved and cooledto 0°÷+5° C. The intermediate cefotaxime acid ethanol solvate (87.5 g)is added and complete dissolution is achieved at 0°÷+5° C. Thetemperature is maintained and 350 ml of ethyl acetate are added over 1hour. The solution is seeded with cefotaxime sodium salt and agitatedfor 1 hour at 0°÷+5° C. A further 263 ml of ethyl acetate are added over40 minutes, then a further 875 ml of ethyl acetate over 1 hour at 0°÷5°C. The mixture is agitated for 30 minutes at the same temperature,filtered and the product washed with 88 ml ethyl acetate and dried at30° C. under reduced pressure. Yield: 80.5 g of cefotaxime sodium salt.

EXAMPLE 4 Preparation Of Ceftiofur Hydrochloride

Two separate solutions are prepared.

Solution A

20 g of Furaca (MW 340.38-58.76 mmol) and 168 ml of tetrahydrofuran arefed into a dry 1 litre flask under a nitrogen flow and in the absence ofdirect light. The mixture is agitated for 15 minutes until homogenizedwhile cooling to +10° C. At +10°÷+12° C. 0.743 ml oftrimethylchlorosilane (MW 108.64-d=0.859) are quickly added. The mixtureis agitated for 5 minutes at +10°÷+12° C. and then 22.72 g BSA(MW=203.43) are added over 5÷10 minutes.

The temperature is raised to +20° C. and the mixture is agitated for 95minutes at +22°÷+23° C. until completely dissolved. It is then cooled to−35°÷−-40° C.

Solution B

105 ml of ethyl acetate and 6.51 ml of dimethylformamide (PM 73.09,d=0.95) are fed into a dry 1 litre flask under a nitrogen flow. At +25°C. 7.75 ml of POCl₃ (MW 153.33, d=1.675) are added, allowing thetemperature to rise to +36° C. over 20÷25 minutes, if necessary heatingit slightly. The mixture is cooled to 0° C. and then 13.81 g of4-chloro-3-oxo-2-methoxyimino-butyric acid, commonly known as COMBA (MW179.56) are added taking care not to exceed +5° C. Agitation ismaintained at +5° C. for 60 minutes.

Solution B is added dropwise into solution A over 15 minutes,maintaining the temperature at −35°÷−40° C. It is left to react for 2hours at the same temperature.

On termination of the reaction the reaction mixture is poured into 100ml of iced water, correcting the pH to 3.0 with about 20 ml oftriethylamine and maintaining the temperature at 0°÷+5° C. Thetemperature is raised to +15°÷+20° C. and the phases are separated. Theaqueous phase is again extracted with 100 ml of ethyl acetate, theorganic phases are pooled and decolorized with 2 g of carbon maintainingagitation for 20 minutes at 15°÷° C. The latter is filtered off, thefilter is washed with 25 ml of tetrahydrofuran and then with 25 ml ofethyl acetate.

The solution is cooled to 0÷+5° C. and 200 ml water at 0÷+5° C. areadded. At the same temperature the pH is corrected to 8 with about 13 mlof triethylamine.

The phases are separated and extracted twice more with 100 ml watermaintaining the pH at 8 with 3 ml of triethylamine. The aqueous phasesare pooled and a solution of benzathine diacetate (27.75 g, MW 360.4) in262.5 ml water is added dropwise over 30 minutes, at 0°÷+5° C., then theremaining benzathine solution left in the dropping funnel is recovered,washing it with water (37.5 ml). Agitation is maintained for 2 hours at0°÷+5° C., then the product is filtered off and allowed to well drain,then finally washed 4 times, each time with 50 ml of water. 112 g ofintermediary product as moist benzathine salt are obtained, with a K.F.of about 60%.

The moist product with the aforestated K.F., is suspended intetrahydrofuran (250 ml) at +20°25° C. 200 g of UBK530 resin in sodiumform and 5.86 g of thiourea are added in the stated order to thesuspension obtained, the pH then being corrected to 8.0÷8.5 withtriethylamine (2.5 ml).

Agitation is maintained for 3 hours at 20°÷25° C., then furthertriethylamine (3.5 ml) is added to correct the pH to 7.5÷8.0. Afterfurther agitation for 20 hours at 20°÷25° C., a final reaction pH of2.5÷3.0 is achieved. The resin is filtered off and washed with 2×50 mlportions of tetrahydrofuran, then twice with a mixture of 25 mltetrahydrofuran+25 ml of ethyl acetate and finally with 25 ml of water.

Triethylamine (7.5 ml) is added to achieve pH 8.0÷8.5 and then ethylacetate (200 ml). The phases are separated and the aqueous phase isdecolorized with 2 g of carbon, adding 0.2 g of EDTA and 0.2 g of celiteand agitating for 20 minutes.

The organic phase is re-extracted with 100 ml of water, which is used towash the filter following decolorization, whereas the organic phase isfinally removed.

125 ml of tetrahydrofuran are added to the decolorized aqueous phase,cooled to 0°÷+5° C. and the pH corrected to 3 with about 60 ml of 1NHCl. 50 g of sodium chloride are then added at the same temperature, themixture is heated to +15°÷+20° C. and the phases are separated.

Water (250 ml) is added to the organic phase and the pH is adjusted to8.0÷8.5 with triethylamine (about 12.5 ml), then ethyl acetate (250 ml)is added.

The phases are again separated, the organic phase is re-extracted withwater (150 ml) at pH 8.0÷8.5 The aqueous phases are pooled, washed 3times with ethyl acetate (200 ml each time), the aqueous phase isdecolorized with 2 g of carbon +0.2 g EDTA+0.2 g celite.

This is filtered off and washed with water (100 ml), the solution iscooled to 0°÷+5° C. and the pH is adjusted to 3 with about 48 ml of 1NHCl. It is agitated while cold for 1 hour, the product is filtered offand washed twice with 100 ml water. It is left to drip well undernitrogen, to obtain 114 g of moist product.

The moist solid is suspended in tetrahydrofuran (125 ml) and agitated at20° C. until dissolution is virtually complete, after about 30 minutes,then a saturated aqueous solution (50 ml) of sodium chloride is addedand further agitated until complete homogenisation of the mixture.

The phases are separated. The organic phase is decolorized with 2 gcarbon at 20° C., filtered and washed with 50 ml tetrahydrofuran. It iscooled to 0°÷+5° C., the pH is corrected to 0.5 with concentrated HCl(about 5.5 ml) and maintained under agitation for 10 minutes at 0°÷+5°C.

The acid solution is added dropwise over 45 minutes to 1500 ml acetonewhile agitated at 20° C. Agitation is continued for a further 60 minutesat 20° C., then the mixture is cooled to 0°/+5° C. and again agitatedfor a further 60 minutes. The product is filtered off and washed with150 ml acetone to obtain 29 g of moist product.

It is dried at 20° C. to obtain 20.5 g of ceftiofur hydrochloride.

Ceftiofur Hydrochloride ¹HNMR

-   9.79 ppm doublet Jcd=8.1 Hz Hc-   8.06 ppm Hn ddd system abc-   7.44 ppm Hm ddd system abc-   6.91 ppm Hl ddd system abc-   6.76 ppm singlet Ha-   5.76 ppm Hd dd Jcd=8.1, Jde=5.16 Hz-   5.16 ppm He doublet Jde=5.16 Hz-   4.27 ppm, 3.93 ppm Hh, Hi system ab two doublets Jhi=13.2 Hz-   3.74 ppm, 3.38 ppm Hf, Hg two doublets system ab-   Jfg=17.6 Hz-   3.92 ppm Hb singlet    Ceftiofur Hydrochloride FT-IR-   amide NH stretching 3273 cm⁻¹-   lactam C═O 1766.3 cm⁻¹-   thioester C═O 1709.0 cm⁻¹-   carboxyl C═O 1659.4 cm⁻¹-   amide C═O 1629.4 cm⁻¹

1. A process for preparing a cephalosporin of formula (I)

in which R¹ is H or Na and R² is chosen from the group consisting of H,CH₃, CH₂OCH₃, CH₂OCOCH₃, CH═CH₂,

according to which a compound of formula (II)

in which R² has the aforestated meanings is silylated at the carboxyl togive the corresponding trialkylsilyl-ester which is reacted with acompound of formula (III)

in which X is Cl or Br and Y is Cl, orO—CH═N⁺(CH₃)₂ Cl⁻ to give a cephalosporin of formula (IV)

in which X and R² have the aforestated meanings, and R³ istrialkylsilyl, which is hydrolyzed at pH 7÷7.5 and then treated in apartly aqueous solution with benzathine or a salt thereof, to obtaincrystallization of a new cephalosporin of formula (V)

where Z is benzathine, in which the carboxyl is salified by thebenzathine, this salt being filtered off, washed with water and reactedin a partly aqueous solvent with thiourea, to lead to the formation ofthe 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic chain and give asolution of the compound of general formula (I) in which R² has theaforestated meanings and R¹ is H, the compound of formula (I) beingcrystallized from this solution in the form of the sodium salt, of thesalt of a pharmaceutically acceptable inorganic acid or of an internalsalt.
 2. A process according to claim 1, wherein simultaneously with theformation of the 2-(2-aminothiazol-4-yl)-2-methoxyyminoacetic chain,there is the precipitation of benzathine hydrochloride which is filteredoff and removed to leave a very pure solution of the compound of generalformula (I).
 3. A process as claimed in claim 1, wherein a product offormula (I) is obtained in which R¹ is H or Na and R² is chosen from thegroup consisting of H, CH₃, CH₂OCH₃, CH₂OCOCH₃, CH═CH₂


4. A process as claimed in claim 2, wherein a product of formula (I) isobtained in which R¹ is H or Na and R² is chosen from the groupconsisting of H, CH₃, CH₂OCH₃, CH₂OCOCH₃, CH═CH₂


5. The benzathine salt of a cephalosporin of formula (V)

where Z, X and R are as specified in claim
 1. 6. A process for preparingthe benzathine salt of a cephalosporin of formula (V) of claim 5,according to which a compound of formula (II)

in which R² has the aforestated meanings, is silylated at the carboxylto give the corresponding trialkylsilyl-ester which is reacted with acompound of formula (III)

in which X is Cl or Br and Y is Cl, orO—CH═N⁺(CH₃)₂ Cl⁻ to give a cephalosporin of formula (IV)

in which X and R² are as specified in claim 1, and R³ is trialkylsilyl,which is hydrolyzed at pH 7÷7.5 and then treated in a partly aqueoussolution with benzathine or a salt thereof, thus obtainingcrystallization of a cephalosporin of formula (V) in which the carboxylis salified by the benzathine, this salt being filtered off and washedwith water.